For the next patch in the game, v0.06, there will be random guests that show up to the inn when certain conditions are met. These girls will not have a storyline/backstory, so can be considered "1-off" characters, with a slightly randomized appearance. Adult content will be available for them. This first implementation of the feature will likely included 6-8 different species of monster girls, and more will be added later.
Please vote for any and all types that you would like to see appearing in the next patch, and the top 6-8 will have a high chance of appearing in the next patch or two.
If there's a monster girl type you really want to see, feel free to add it in the comments below!